FR2989017A1 - Method for molding e.g. mask between surfaces of fixed and moving parts of mold, utilized in lighting and/or signaling device of car, involves holding plastic part in contact with moving part during separation of fixed part from moving part - Google Patents

Abstract

The method involves holding a plastic part (4) in contact with a moving part (3) of a mold during separation of a fixed part (2) of the mold from the moving part. A maintenance element (33) of the plastic part is installed on the moving part. The maintenance element is movably fixed with respect to the moving part. The plastic part is released from the mold by displacing a unit including the moving part and the part solidified with respect to the fixed part and by displacing the plastic part with respect to the moving part. Independent claims are also included for the following: (1) a plastic part (2) a lighting and/or signaling device of a car (3) a mold.

Description

Method of molding a lighting or signaling device part for a motor vehicle The present invention relates to a method of molding a workpiece between a first surface of a first portion of a mold and a second surface of a second portion of the mold. The invention relates in particular to the molding of a part of a lighting and / or signaling device of a motor vehicle, in particular to the molding of an aspect part of such a device, in particular to molding a mask of such a device. The invention also relates to a part, in particular a mask of a lighting and / or signaling device, obtained by such a molding process. The invention also relates to a mold for producing a workpiece and comprising a first mold part having a first surface and a second mold part having a second surface, the first and second surfaces delimiting a molding cavity. In the field of the manufacture of lighting and / or signaling devices for a motor vehicle, it is common to produce parts by molding. It is particularly common to make plastic parts by molding. These parts may especially be masks, or even reflectors. It follows that their appearance, at least on one of their faces, must be very neat. In addition, there are problems in this molding technology of plastic parts. Indeed, due to the removal of the material during the solidification of the parts in the mold, the faces of the part will be in contact with the surfaces of the mold, or even stick against them, and, consequently, the The appearance of these faces may be altered during demolding, in particular during the movement of the face relative to the mold surface on which the face is supported. It is common to see scratches or scratches appear on this level. It is understood that this kind of defect is incompatible with the aesthetic and / or optical functions provided in particular by a lighting device mask and / or signaling or a reflector of lighting and / or signaling device.

To remedy this problem, it is known to make particular shapes in the molds having consequences on the geometry of the parts made, including creating shapes with important remains, creation of reservoirs, adding ribs or granite.

Alternatively or additionally, it is possible to provide a demolding operation by movement to limit the problem. It is possible to provide a slider against undercut. However, in some cases, these changes in shape of the part are not possible, because of the style chosen for the part or because of other components coming close to the part. Furthermore, the movement demolding operation, the use of an undercut slider may not be economically feasible. The object of the invention is to provide a molding process remedying the disadvantages mentioned above and improving the molding processes known from the prior art. In particular, the invention proposes a simple, economical molding method that makes it possible to avoid damage to the faces of the molded parts produced during the demolding operation, while retaining great freedom in producing the shapes of the molded parts. The invention also relates to a mold for carrying out such a molding process. For the invention, the method enables a part to be molded between a first surface of a first portion of a mold and a second surface of a second portion of the mold. The method comprises a step of demolding the workpiece comprising maintaining the workpiece in contact with the second mold part when the first part of the second part is moved apart. Thus, during the solidification of the workpiece and after solidification of the workpiece, the workpiece is kept at a distance from the first mold part. Consequently, it is possible to unmould the part without risk of damaging the surface condition of a face of the part produced.

The step of holding the workpiece may include placing at least one workpiece holding member on the second mold portion. The at least one holding element may be fixedly mounted or may be movably mounted relative to the second mold part.

The demolding step may comprise a displacement of an assembly comprising the second mold part and the solidified part relative to the first mold part.

The demolding step may comprise a movement of the workpiece relative to the second mold part. This displacement of the part relative to the second mold part is advantageously obtained by the action of an ejector, in particular an ejector comprising at least one holding element.

The invention also relates to a part obtained by the implementation of the molding method defined above. According to the invention, a lighting and / or signaling device of a motor vehicle comprises a part, in particular a part of appearance such as a mask, defined above.

According to the invention, the mold is intended for the production of a workpiece and comprises a first mold part having a first surface and a second mold part having a second surface, the first and second surfaces delimiting at least in part a cavity molding. The second mold part comprises at least one element for holding the workpiece on the second mold part, the at least one holding element keeping the workpiece in contact with the second mold part when the first part is moved apart of the second part.

The at least one holding element may be fixed or movable relative to the second mold part, in particular mounted on an ejector in mechanical connection with the second part.

The at least one holding element may comprise a protrusion extending from a wall of the cavity, for example perpendicular to the thickness of the cavity. In particular the projection may extend in the direction of movement of the first part relative to the second part.

The distance separating the projection from the second surface may be less than the distance separating the projection from the first surface. In particular, the distance separating the projection from the second surface may be at least 30% less than the distance separating the projection from the first surface. Thus, the molded part can be held against the second surface or in contact with the second surface and thus at a distance from the first surface. It follows that during the demolding step, the first mold part can be moved relative to the assembly formed by the second mold part and the molded part without the first mold part rubbing on the molded part. .

The invention also relates to a motor vehicle comprising a lighting and / or signaling device defined above.

The attached drawings show a non-limiting example of embodiment, in which: FIG. 1 is a sectional view of a first embodiment of a mold according to the invention, FIG. 2 is a detail view in section of the first embodiment of the mold according to the invention, FIG. 3 is an exploded perspective view of a lighting and / or signaling device comprising a mask made by an embodiment of the molding method according to the invention. FIG. 4 is a detailed sectional view of an alternative embodiment of a mold according to the invention comprising an ejector, FIG. 5 is a detail sectional view of a mask wall produced by a known molding process. of the prior art, Figure 6 is a detail sectional view of a mask wall made by an embodiment of the molding method according to the invention. A first embodiment of a mold 1 according to the invention is described hereinafter with reference to FIGS. 1 and 2. Such a mold 1 makes it possible to mold a part 4 of a lighting and / or signaling device for motor vehicle. In particular, it makes it possible to mold a part made of plastic material, in particular a mask 4 or a reflector. The plastic material is, for example, PBT polyethylene terephthalate, the average surface shrinkage of which is 2%.

The mold 1 comprises a first mold part 2, in particular a fixed mold part, having a first surface 24 and a second mold part 3, in particular a moving mold part, having a second surface 34. The first and second surfaces delimit a mold cavity 40 defining the shapes of the part. The first and second surfaces are at least substantially parallel.

The second mold part comprises at least one element 33 for holding the part on the second mold part, the at least one holding element keeping the part at a distance from the first mold part, in particular at a distance from the first surface of the first mold part during the solidification of the workpiece and after the solidification of the workpiece. Thus, during the step of demolding the workpiece, the element 33 keeps the workpiece in contact with the second mold part when the first part of the second part is moved apart. In the first embodiment, the workpiece 33 at least one holding element is fixedly mounted on the second mold part. Preferably, the at least one holding element is formed on a member 31 attached to the second mold part. For example, the attached member can be embedded in the second mold part and be fixed with a screw 32.

The at least one holding element preferably comprises a projection 33 extending into the cavity, from a wall of the cavity, preferably it extends in the demolding direction. Thus, the projection extends inside the material and / or in the extension of the surface 34 in the demolding direction. It is limited in height to ensure that it does not cause appearance defects. Preferably, the distance separating the projection 33 from the second surface 34 is smaller than the distance separating the projection from the first surface 24.

In particular, the distance separating the projection from the second surface may be at least 30% less than the distance separating the projection from the first surface. The minimum of this distance is determined so that the filling by the plastic is correct and that the strength of the mask is sufficient at this level to ensure proper demolding. The maximum of this distance is determined for thickness to avoid appearance defect, including shrinkage and thickness variation effect). In the example of Figure 2, for a piece thickness e of about 2.4 mm, there is a projection width of about 0.8 mm, a distance between the projection 33 of the second surface 34 of about 0.5 mm and a distance separating the projection from the first surface of approximately 1.5 mm (dimensions measured perpendicular to the first surface at the edge of the cavity defining the edge 44 of the part 4. Furthermore, the height of the projection may be approximately 1.8 mm This projection makes it possible to define or separate on the part made two lips 45 and 46 arranged on either side of the projection, preferably the height of the projection is greater than the value of withdrawal of the piece. Preferably, the height of the lip 46 between the projection and the second surface 34 is greater than the height of the lip 45 between the projection and the first surface 24. For example, in FIG. of the lip lying between the protrusion and the second surface is about 1.1 mm and the width of this lip is about 1.5 mm while the height of the lip lying between the projection and the first surface is about 1.5 mm and the width of this lip is about 0.5 mm.

A second embodiment of the mold is described below with reference to FIG. 4. This second embodiment differs from the first embodiment in that the at least one holding element is made on an ejector 31 'implanted in the second mold part. This ejector makes it possible to deposit the solidified part of the second mold part at the end of molding. A third embodiment of the mold is described hereinafter with reference to FIG. 6. This third embodiment differs from the first embodiment in that the edge 44 'of the solidified part 4' has a geometry such that it remains clipped on the second part of the mold. At this edge 44 ', the lips 45' and 46 'and the groove 47' have a geometry different from those of the first embodiment. Thus, a mechanical action of a low intensity must be exerted in order to deposit the piece of the second mold part.

Preferably, the mold comprises a plurality of holding elements as described above. Preferably, these holding elements are distributed over the second mold part. They are preferably distributed in such a way that they are arranged regularly or uniformly relative to the edge 44 of the part 4.

The mold makes it possible to produce the part 4, in particular the mask 4, represented in FIG. 3. To do this, one embodiment of the molding method according to the invention must be implemented. This part comprises a first edge 44, a second edge 43, an inner face 42 and an outer face 41.

The mold described above produces at the edge 44 at least locally one or more grooves 47 made due to the presence of one or more projections 33 in the mold cavity. The mask 4 may be part of a lighting and / or signaling device as shown in FIG. 3. In this figure, the lighting and / or signaling device comprises a housing 101 closed by a closure glass 102. The set consisting of the housing and the ice housing: - an optical device comprising a light source and at least one shaping element of a light beam produced by the light source; and the mask 4. Preferably, the edge 44 of the mask is arranged relative to the optical device and the edge 43 of the mask is mechanically connected to the housing 101.

One embodiment of the molding method according to the invention is described below with reference to FIGS. 1, 2, 4 and 6.

In a first step, the first mold part and the second mold part are assembled so that the shapes of the molding part 4; 4 'are defined by the geometry of a cavity 40 made between the first and second mold parts. In particular, the geometry of the cavity is defined by a first surface of the first portion and a second surface of the second portion. In a second step, molten material is introduced into the cavity in order to produce the part. In a third step, during the solidification of the workpiece and after solidification of the workpiece, the workpiece is kept at a distance from the first mold part, in particular from the first surface of the first mold part during the solidification of the workpiece. piece and after the solidification of the piece. This is achieved thanks to the at least one holding element present on the mold, in particular on the second mold part, and previously described. To do this, the element 33 keeps the workpiece in contact with the second mold part.

To do this, the at least one element 33 for holding the workpiece on the second mold part has been placed beforehand in the mold, in particular on the second mold part.

As seen above, the at least one holding member is fixedly mounted or is movably mounted relative to the second mold part. Once the part has solidified, the demoulding may take place as follows: an assembly comprising the second mold part and the solidified part relative to the first mold part is displaced, for example in the direction and direction indicated by the arrow A on FIG. 1, then moves the workpiece relative to the second mold part in the direction and the direction indicated by the arrow B in FIG. 1. The second displacement can be obtained by the action of an ejector, in particular of an ejector comprising at least one holding element 33. The effect of the at least one holding element is described below with reference to FIGS. 6 and 7. FIG. 5 shows a partial sectional view. of the cavity of a mold known from the prior art. After filling the cavity with the molten material, this material solidifies to form the part 4. As a result of the removal of material, the solidified part does not occupy the entire cavity formed by the mold. day (or space) appears between the face 43 "of the workpiece 4" and the surface 34 "of the second mold part. On the other hand, also due to the removal of material, the face 42 "of the part 4" sticks on the surface 24 "of the first part of the mold, so that the surface state of the face 42" of the mold is understood. the part may be damaged during demolding. This is all the more problematic if the face 42 "of the piece is then intended to be visible and / or has an aesthetic function.In FIGURE 6, a partial sectional view of the cavity of a mode is shown. According to the invention, after filling the cavity with the molten material, this material solidifies to constitute the piece 4 '. Due to the removal of material, the solidified part does not occupy the entire In fact, the material solidifies around the projection 33 'and one day (or a space) appears between the face 42 of the part 4 and the surface 24 of the first part of the mold. To do this, the projection 33 'has a height greater than the value of the shrinkage of the workpiece, It is understood that the workpiece is then kept at a distance from the first mold part, in particular at a distance from the first workpiece surface. of mold, during the solidification of the pi and after the solidification of the piece. It is then understood that the release of the part 4 can be achieved without risk of altering the surface condition of the face 42 of the part. Indeed, during the demolding step of the workpiece, the element 33 keeps the workpiece in contact with the second mold part when the first part of the second part is moved apart. Thus, the face 42 can easily be a face having an aesthetic function. Note that, to move from the room shown in Figure 5 to the room shown in Figure 6, only changes the geometry of the room without changing the volume of the room. The geometry is studied to avoid any defect in the part obtained, in particular to avoid defects of the type of shrinkage, which appear during the increase of the volume of the parts.

The materials used to make parts are for example polycarbonate type or semi-crystalline type, such as polyamide or PBT. The materials used may have significant shrinkage rates during solidification, for example of the order of 2%.

The solution described allows a good maintenance molding position of the plastic part area and thus avoids any risk of creating scratches caused by sticking adhesion phenomena and withdrawal during the opening phase of the mold.

As seen above, a shape is used as a projection or a rib entering the thickness of the part to be produced. To limit the penetration height of this projection or rib and only if the visual aspect allows it, it is recommended to provide a sufficient thickness of material between the projection or rib and the second surface of the second mold part.

In order to avoid a lack of appearance (of the type of shrinkage, deformation, etc.) caused by the presence of the projection or rib, it is also sought for a maximum thickness of material between the projection or rib and the first surface of the first part of mold. It is necessary to thicken the part and / or to adapt the geometry to be produced in the vicinity of the holding element. The dimensioning of the mold must take into account the differences between the geometry of the mold including the shrinkage value taken into account for machining and the part according to its theoretical definition possibly supplemented with a deformation value if such a risk is identified. The molding method according to the invention is particularly suitable for the production of parts having substantially conical shapes with small bodies and whose inner faces have aesthetic and / or optical functions. Throughout this text, the term "at least substantially" used with different adjectives means: "adjective" or "substantially adjective", for example "at least substantially perpendicular" means "perpendicular" or substantially perpendicular.

Claims (1)

CLAIMS1- A process for molding a workpiece (4; 4 ') between a first surface (24) of a first part (2) of a mold (1; 1') and a second surface (34) of a second part (3) of the mold, comprising a step of demolding the workpiece comprising a holding of the workpiece in contact with the second mold part when the first part of the second part is moved apart. Molding method according to the preceding claim, characterized in that the step of holding the workpiece comprises placing at least one element (33) for holding the workpiece on the second mold part. Molding method according to the preceding claim, characterized in that the at least one holding element is fixedly mounted relative to the second mold part. Molding method according to claim 2, characterized in that the at least one holding element is mounted movably relative to the second mold part. Molding method according to one of the preceding claims, characterized in that the demolding step comprises a displacement of an assembly comprising the second mold part and the solidified part relative to the first mold part. Molding method according to the preceding claim, characterized in that the demolding step comprises a movement of the workpiece relative to the second mold part. 7- 8- 9- 10- 20 11- 25 12- 30 14 Molding process according to the preceding claim, characterized in that the displacement of the piece relative to the second mold part is obtained by action of an ejector, in particular an ejector comprising at least one holding member. Part (4; 4 ') obtained by the implementation of the molding method according to one of the preceding claims. Device (100) for lighting and / or signaling a motor vehicle comprising a part, in particular a part of appearance such as a mask, according to the preceding claim. Mold (1; 1 ') for producing a workpiece (4; 4') and comprising a first mold part (2) having a first surface (24) and a second mold part (3) having a second surface (34), the first and second surfaces defining at least partly a molding cavity, characterized in that the second mold part comprises at least one element (33) for holding the workpiece on the second mold part, at least one holding element keeping the workpiece in contact with the second mold part when the first part of the second part is moved apart. Mold according to the preceding claim, characterized in that the at least one holding element is fixedly mounted relative to the second mold part, in particular mounted on an ejector in mechanical connection with the second part. Mold according to claim 10, characterized in that the at least one holding element is mounted movably relative to the second mold part, in particular mounted on an ejector in mechanical connection with the second piece. Mold according to claim 10, 11 or 12, characterized in that the at least one holding element comprises a projection (33) extending from a wall of the cavity, in particular a projection extending in the direction of movement of the first part relative to the second part. 14- The mold of claim 13, characterized in that the distance separating the projection (33) of said second surface (34) is less than the distance separating the projection (33) of said first surface (24), in particular in that the distance separating the projection (33) from said second surface (34) is at least 30% less than the distance between the projection (33) and said first surface (24).